The invention relates to a channel estimation method, and in particular, to an apparatus and method for approximating the channel response in a telecommunication system.
In telecommunication systems, the characteristics of the transmission channel can be represented by a channel response h[n]=[h0, h1, . . . , hN]. As is well known in the art, the channel estimation is an important task for a receiver. Traditionally, channel estimators are divided into two categories: data aided and non-data aided (blind) estimators. Data aided channel estimators operate on a pre-specified set of transmitted symbols that are known to the receiver. These symbols do not convey any information and are often called “pilot symbols” or “training sequences”. Data aided channel estimators are typically simple to implement and relatively robust. Their major disadvantage is that they lead to an overall reduction in system throughput, since some of the transmitted symbols (the pilot symbols) do not carry any information.
Non data aided channel estimators, on the other hand, do not reduce the system throughput. However, they are typically quite complicated to implement as they are often based on higher order statistics of the received signal, and they most often suffer from high statistical variability, i.e. they suffer from large estimation errors. Generally, the accuracy of the channel estimation is important for correctly receiving, decoding the received signal. However, in some cases the required accuracy of the channel estimation is not so high. For example, the equalizer in the receiver may just want to roughly know the location and the strength of each echo in a multipath channel so that the initial step size for each equalizer coefficient for performing the adaptive algorithm can be determined accordingly. Therefore, it is desired that the channel estimation mechanism can somehow be simplified to reduce the implementation cost.